1. Field of the Invention
The invention relates generally to agricultural machines, in particular agricultural machines having driven processing members such as mowers, tedders or rotary harrows. The invention further relates to a method of overload protection for such machines.
2. Description of the Related Art
In general, in agriculture there is a trend to enlarge the machines in use in order thus to enable more efficient agricultural operation on a piece of land. With agricultural machines comprising rotating processing members this leads typically to an increasingly larger working width, and an increasing number of processing members being arranged in one row.
During processing ground or a crop which is lying on the ground it is possible that one of the processing members becomes stuck on an obstacle, for example a pole, tree or large stone. It will then suddenly no longer be possible for the processing member in question to rotate, while it is still being driven by the associated drive shaft. As a result thereof, the load which is exerted on the drive mechanism of the agricultural machine will suddenly increase quickly, resulting in a great risk of damage of the drive. In particular, there may be a great risk of the gear wheels of a transmission being damaged as a result of an overload.
It is known to place an overload protection on the main drive mechanism of a drive device in order to disconnect, in response to a suddenly increasing load, the drive mechanism from the driving source, for example the motor of a tractor, in order to limit the maximum load and thus to prevent damage of the drive mechanism.
However, in particular in the case of larger agricultural machines, in which a larger number of processing members should be driven simultaneously, the mass moment of inertia of the drive device and the processing members is accordingly greater. Suddenly stopping such a large mass which is interconnected via the drive mechanism may still provide a momentary load which may lead to damage of the drive mechanism. Moreover, an increased number of processing members also results in an increased total load which is required for driving all processing members. As a result, the components of the drive mechanism should be designed to be stronger.
In order to prevent the drive mechanism from being damaged, it could be possible, by means of an overload coupling, to disconnect only the blocked processing member from the drive mechanism at a too great load, so that the other processing members would be free to continue to rotate. However, this is only possible if the paths of movement of the processing members do not overlap. In a number of cases however, such as embodiments of mowers, tedders or rotary harrows, the paths of movement of the processing members overlap. For example, in the case of a specific type of tedder, each of the processing members may comprise arms with tines fastened thereto. The arms are arranged with respect to each other in such a manner that the arms of adjacent processing members rotate between each other. The processing members thus have overlapping paths of movement and should, therefore, be moved synchronously.
If, in such an agricultural machine, only the processing member which is suddenly blocked is disconnected, the arms of the adjacent processing member will run into the arms of the blocked processing member. This may lead to damage of the arms, for example serious deformation or breakage of the arms or the tines attached thereto. In such an agricultural machine, such a single disconnection of a single processing member is therefore unwanted.
EP 1 258 187 A2 discloses a drive mechanism for agricultural machines comprising a main drive shaft and two drive sections for driving a group of processing members. Each drive section comprises a drive shaft and an overload coupling which, in the case of an overload, falls back to a minimum torque value. The drive shafts are in line. A catching device is provided between the drive shafts. The catching device is a device to allow a maximum angular rotation between the two drive shafts and consequently the groups of processing members.
When one of the processing members is blocked by an obstacle, the group of processing members in question is completely blocked and disconnected from the drive mechanism by means of the overload coupling. However, the other group of processing members continues to rotate until the catching device does not allow further relative rotation because a maximum angular rotation has been reached. Consequently, the second group of processing members will also be blocked and the overload coupling present in this drive section will be disengaged. By using this drive mechanism, the processing members will not be stopped in one go, but in two phases.
A further advantage of the drive mechanism according to EP 1 258 187 A2 is that the load is distributed over the two drive sections, in which case there is provided for each drive section an overload coupling with a maximum load of 50% of the maximum load of the main drive shaft. However, as a result of the fact that the two drive shafts of the two drive sections are in operative connection with each other by means of the catching device, two peak loads will occur in the blocked drive section.
Thus, there is a particular need for an alternative drive mechanism for an agricultural machine, which reduces the risk of damage of the drive mechanism or processing members in the case of an overload of one or more of the processing members.